Nonlinear optimal control for the five-phase induction motor-based traction system of electric vehicles

• Published in: Compel 2024-03, Vol.43 (1), p.167-191
• Main Authors: Rigatos, Gerasimos G., Siano, Pierluigi, Al-Numay, Mohammed S., Sari, Bilal, Abbaszadeh, Masoud
• Format: Article
• Language: English
• Subjects: Asymptotic properties; Automobiles; Control algorithms; Control methods; Control systems design; Dynamic models; Dynamical systems; Electric vehicles; Exhaust gases; Fault tolerance; Feedback control; H-infinity control; Induction motors; Jacobi matrix method; Linearization; Multiphase; Nonlinear control; Nonlinear systems; Optimal control; Optimization; Permanent magnets; Phases; Present value; Series expansion; Synchronous motors; Taylor series; Traction
• ISSN: 0332-1649; 2054-5606; 0332-1649
• DOI: 10.1108/COMPEL-05-2023-0186

Purpose The purpose of this article is to treat the nonlinear optimal control problem in EV traction systems which are based on 5-phase induction motors. Five-phase permanent magnet synchronous motors and five-phase asynchronous induction motors (IMs) are among the types of multiphase motors one can consider for the traction system of electric vehicles (EVs). By distributing the required power in a large number of phases, the power load of each individual phase is reduced. The cumulative rates of power in multiphase machines can be raised without stressing the connected converters. Multiphase motors are also fault tolerant because such machines remain functional even if failures affect certain phases. Design/methodology/approach A novel nonlinear optimal control approach has been developed for five-phase IMs. The dynamic model of the five-phase IM undergoes approximate linearization using Taylor series expansion and the computation of the associated Jacobian matrices. The linearization takes place at each sampling instance. For the linearized model of the motor, an H-infinity feedback controller is designed. This controller achieves the solution of the optimal control problem under model uncertainty and disturbances. Findings To select the feedback gains of the nonlinear optimal (H-infinity) controller, an algebraic Riccati equation has to be solved repetitively at each time-step of the control method. The global stability properties of the control loop are demonstrated through Lyapunov analysis. Under moderate conditions, the global asymptotic stability properties of the control scheme are proven. The proposed nonlinear optimal control method achieves fast and accurate tracking of reference setpoints under moderate variations of the control inputs. Research limitations/implications Comparing to other nonlinear control methods that one could have considered for five-phase IMs, the presented nonlinear optimal (H-infinity) control approach avoids complicated state-space model transformations, is of proven global stability and its use does not require the model of the motor to be brought into a specific state-space form. The nonlinear optimal control method has clear implementation stages and moderate computational effort. Practical implications In the transportation sector, there is progressive transition to EVs. The use of five-phase IMs in EVs exhibits specific advantages, by achieving a more balanced distribution of power in the multiple phases of the mot